This clinical trial investigates the efficacy of combining orthokeratology (OK) lenses with repeated low-level red-light (R.L.R.L.) therapy in slowing the progression of myopia in children classified as ortho-k non-responders. The MADRID study is a single-centre, prospective, randomized controlled trial conducted at the Centro Fernández-Velázquez in Madrid, Spain. Participants aged 8 to 15 years will be randomly assigned to either a control group (OK lenses only) or an experimental group (OK lenses + R.L.R.L. therapy). The primary objective is to assess the potential additive effect of R.L.R.L. therapy on axial length control over a 6 to 12-month follow-up period. All participants will undergo ocular biometry and posterior segment OCT at regular intervals. The study is fully self-funded by the institution and adheres to rigorous ethical and safety standards.

Background and Rationale Myopia is a growing public health concern worldwide, especially among children, due to its progressive nature and association with severe ocular complications later in life. Orthokeratology (OK) lenses are one of the most effective non-pharmacological interventions for myopia control, reducing axial elongation by up to 63%. However, a subset of children, referred to as "ortho-k non-responders", continue to exhibit rapid axial elongation despite consistent use of OK lenses.

Repeated low-level red-light (R.L.R.L.) therapy is a novel, non-invasive intervention that has shown promise in reducing myopia progression. Preliminary studies suggest its mechanism may involve choroidal thickening, potentially complementing the effects of OK lenses. This study seeks to evaluate whether the combination of OK and R.L.R.L. offers additive benefits in myopia control for this specific population.

Study Design and Objectives This is a prospective, single-centre, randomized controlled clinical trial. The trial is being conducted at the Centro Fernández-Velázquez (Madrid, Spain) and aims to recruit 10 participants aged 8-15 years who meet specific inclusion criteria, including documented poor response to orthokeratology alone.

Participants will be randomized into two groups:

Experimental Group: OK lens + R.L.R.L. therapy (2 sessions/day, 3 minutes/session, minimum 4-hour interval) Control Group: OK lens only The primary endpoint is the change in axial length over 6 months, with the possibility of extending the intervention and monitoring for up to 12 months. Secondary endpoints include changes in refractive error, choroidal thickness, and treatment tolerance.

Measurements and Timeline Axial length will be measured using the Oculus Myopia Master. Posterior segment imaging will be performed with Topcon Maestro OCT. All evaluations are scheduled at baseline, 1 month, 3 months, and 6 months, and-if extended-at 9 and 12 months. All measurements will be performed between 9 a.m. and 11 a.m. to minimize diurnal variation.

Safety and Ethics All participants and/or their guardians will sign an informed consent prior to enrollment. The study adheres to the principles of the Declaration of Helsinki. A detailed adverse event management and reporting protocol is in place. All serious adverse events (SAEs) will be reported to the relevant ethical committees within 72 hours.

Funding and Conflicts of Interest This trial is fully self-funded by the Centro Fernández-Velázquez. The investigators declare no financial or personal conflicts of interest.

Conclusion This study will provide important preliminary evidence on the combined use of OK lenses and red-light therapy in managing progressive myopia in children who are non-responsive to orthokeratology alone. If effective, this combined approach could be incorporated into standard care protocols for high-risk paediatric patients.

Inclusion Criteria:

• Children aged 8 to 15 years. Intention to undergo orthokeratology (OK) lens treatment. Spherical equivalent refractive error between -1.00 and -4.00 diopters in either eye.

Astigmatism no greater than 1.50 D in either eye. Best corrected visual acuity (BCVA) of 25/25 or better in both eyes. Birth weight of at least 1500 g. Classified as ortho-k non-responders: continued OK use with persistent rapid myopia progression.

Willingness of child and legal guardian to participate and attend follow-up visits.

Signed informed consent by parent or guardian.

Exclusion Criteria:

• cular conditions such as strabismus, amblyopia, cataract, or ptosis. Previous use of OK lenses or atropine for myopia control. Contraindications to atropine (e.g., known allergy, cardiovascular disease, epilepsy).

Ocular contraindications to OK lens wear (e.g., inflammation, infection). Systemic diseases that may affect ocular growth (e.g., Down syndrome, Marfan syndrome).

Any other ocular disease that could interfere with study outcomes.

Individual participant data (IPD) will not be shared for this study due to the small sample size, the exploratory nature of the investigation, and privacy considerations. Future larger-scale studies may consider data sharing under appropriate governance.